(a) Field of the Invention
The present invention relates to a novel sulfonium salt compound employable as a photo-acid generator for a chemically amplified photoresist material, a chemically amplified photoresist composition using the novel sulfonium salt compound as the photo-acid generator, and a method for patterning by using the photoresist composition. More concretely, the present invention relates to the novel sulfonium salt compound suitably used as the photo-acid generator for the chemically amplified photoresist material having an exposing wavelength in a range from a far ultraviolet ray to a vacuum ultraviolet ray having a wavelength between 130 nm and 220 nm.
(b) Description of the Related Art
Higher density, higher integration or higher speed is required in a highly integrated circuit element represented by a semiconductor device such as a DRAM (dynamic random access memory). Accompanied thereby, the establishment of the fine processing technology in a range of half-micron order, for example, the photolithographic technology for forming fine patterns is required more and more stringently in the field of manufacturing electronic devices.
A process of implementing the fine patterns in the photolithographic technology includes the shortening of a wavelength of an exposing ray used in the formation of the patterned resist. Generally, the degree of optical resolution (R) can be represented by the Rayleighs equation, that is, R=kxc2x7xcex/NA (wherein xcex is a wavelength of an exposing ray, NA is numerical aperture and xe2x80x9ckxe2x80x9d is a process factor). In order to progress the formation of fine patterns, the higher optical resolution is required in the optical system used therein, or the wavelength xe2x80x9cxcexxe2x80x9d of the exposing ray is shortened for reducing the degree of the resolution xe2x80x9cRxe2x80x9d of the optical system.
In the manufacture of a DRAM of 256 megabits, for example, the degree of resolution of line-and-space having the minimum pattern dimension of 0.22 xcexcm is required, and a KrF excimer laser (wavelength: 248 nm) is used as a light source. In the manufacture of an advanced DRAM of 1 gigabit or more, the patterning dimension becomes 0.15 xcexcm or less requiring the finer processing technique, and an ArF excimer laser (wavelength: 193 nm) and an F2 excimer laser (wavelength: 157 nm) having a shorter wavelength ray (a far ultraviolet ray and a vacuum ultraviolet ray) are efficiently utilized and required. Currently, the lithography using the ArF excimer laser is extensively researched [refer to Journal of Photopolymer Science and Technology, vol.9, no.3, p.387 to 397 (1996)].
In the use of the ArF excimer laser and the F2 excimer laser, the higher sensitivity is requested in the development of resist for exposure in addition to the higher resolution responding to the fine processing dimension because the lifetime of a gas used in these lasers is short and the damage of a lens generated by a laser ray is large. A chemically amplified photoresist is well known utilizing a photo-acid generator as a sensitized material for obtaining the higher sensitivity of the resist. A representative example is described in JP-A-2(1990)-27660 showing a resist formed by a combination of poly(p-tert-butoxy carbonyloxy-xcex1-methylstyrene) and triphenylsulfonium hexafluoro-arsenate acting as a photo-acid generator. The chemically amplified photoresist is currently used for the KrF excimer laser [for example, refer to Hiroshi Ito and C. Grantwilson, American Chemical Society Symposium Series, vol.242, p.11 to 23 (1984)].
The chemically amplified photoresist characteristically generates a protonic acid from the photo-acid generator contained therein by means of irradiation of light, and the protonic acid reacts with resist resin under existence of an acid catalyst by a thermal treatment after exposure. By using the acid catalysis, the considerably higher sensitivity can be attained compared with a conventional resist having a photoreaction efficiency (reaction per one photon) of 1 or less. Most of the resists currently developed are chemically amplified ones. An example of the photo-acid generator currently used includes a triphenyl- sulfonium salt derivative developed by J. V. Crivello described in J. Org.Chem., vol.43, no.15, p.3055 to 3058 (1978).
A representative example of the photo-acid generator currently used in the chemically amplified resist for the ArF excimer laser already proposed is the triphenylsulfonium salt derivative [refer to, for example, Nozaki, et al., Journal of Photopolymer Science and Technology, vol.10, no.4, p.545 to 550 (1997) or Yamachika, et al., Journal of Photopolymer Science and Technology, vol.12, no.4, p.553 to 560 (1999)]. Since, however, these triphenylsulfonium salt derivatives strongly absorb light having a wavelength of 220 nm or less, the transparency of the resist is reduced to lower the resolution when the triphenylsulfonium salt derivative is used as the photo-acid generator [refer to, for example, Takuya Naito, 8 th Optical Reaction and Electronic Material Research Course, Lecture Brief, p.16 to 18 (1999)].
Accordingly, one of the technical problems currently researched in the development of the resist material suitable for exposure to a light having a wavelength of 130 to 220 nm representatively used in the ArF excimer laser is the development of the photo-acid generator having a higher photoreaction efficiency (photo-acid generation efficiency) and a higher transparency to an ultraviolet ray of a wavelength of 220 nm or less.
In view of the foregoing, an object of the present invention is to provide a novel photo-acid generator or a novel sulfonium salt compound utilized in a chemically amplified resist material suitable for a light having a wavelength of 130 to 220 nm representatively used in the ArF excimer laser, and more in detail, to the novel photo-acid generator having a higher transparency to an ultraviolet ray of a wavelength of 220 nm or less and a higher photoreaction efficiency (photo-acid generation efficiency).
Another object of the present invention is to provide a chemically amplified resist composition containing the novel photo-acid generator.
A further object of the present invention is to provide a method for patterning by using the photoresist composition.
The present invention provides, in a first aspect thereof, a sulfonium salt compound designated by a general formula (I), 
wherein R1 and R2 are independently selected from the group consisting of a linear alkyl group, a branched alkyl group, a monocyclic alkyl group and a cross-linked cyclic alkyl group, or R1 and R2 having the saturated alkyl group are linked to each other forming a ring or R1 and R2 are linked to each other forming a ring having a substituted oxo group, R3, R4, R5 and R6 are independently selected from the group consisting of a hydrogen atom, a halogen atom, an alkyl group and an alkoxy group having 1 to 4 carbon atoms, X is selected from the group consisting of xe2x80x94CH2xe2x80x94, xe2x80x94C2H4xe2x80x94 and xe2x80x94OCH2xe2x80x94 (wherein an oxy group is bonded to a benzene ring), and Yxe2x88x92 is a counter ion.
The present invention provides, in a second aspect thereof, a method including the steps of: forming a photoresist layer by application of the sulfonium salt compound of the present invention as described above as a positive photoresist material or a negative photoresist material on an underlying layer to be patterned; transferring a desired pattern to the photoresist film on a photoresist composition by exposing the photoresist layer to light having a wavelength between 130 and 220 nm; baking the photoresist layer: and developing the photoresist layer to form a photoresist pattern.
In accordance with the first and the second aspects of the present invention, the sulfonium salt compound having 1-oxoindan-2-yl group or a similar group can be used as a photo-acid generator which is excellent in transparency in a range from a far ultraviolet ray to a vacuum ultraviolet ray having a wavelength between 130 nm and 220 nm. Accordingly, the photoresist composition using the sulfonium salt compound of the present invention as the photo-acid generator has a higher sensitivity and a higher resolution with respect to the exposure light in the range from the far ultraviolet ray to the vacuum ultraviolet ray having a wavelength between 130 nm and 220 nm, thereby facilitating the fine pattern formation in the manufacture of a semiconductor device.
The above and other objects, features and advantages of the present invention will be more apparent from the following description. PREFERRED EMBODIMENTS OF THE INVENTION
Now, the present invention is more specifically described.
After producing various novel sulfonium salt compounds and examining the properties thereof, the present inventors have found that a sulfonium salt compound of the following general formula (I) containing, in place of various phenyl groups in a conventional triphenyl sulfonium salt derivative, 1-oxoindan-2-yl group, various substituted 1-oxoindan-2-yl groups, 1-tetralone-2-yl group, various substituted 1-tetralone-2-yl groups, 4-chromanone-2-yl group or various substituted 4-chromanone-2-yl groups has a higher photoreaction efficiency (photo-acid generation efficiency) and an excellent transparency with respect to an ultraviolet ray having a wavelength of 220 nm or less, and have reached to the present invention.
The sulfonium salt compound of the present invention has a structure specified in the above general formula (I) and includes a cyclic group selected from the group consisting of 1-oxoindan-2-yl group, various substituted 1-oxoindan-2-yl groups, 1-tetralon-2-yl group, various substituted 1-tetralon-2-yl groups, 4-chromanon-2-yl group and various substituted 4-chromanon-2-yl groups, and various alkyl groups designated by R1 and R2. The exposure is conducted by the absorption originated from the cyclic groups. Since the other absorption originated from the remaining R1 and R2 groups is quite small in the wavelength range between 130 and 220 nm, the sulfonium salt compound of the present invention exhibits the excellent transparency with respect to the ultraviolet ray having the wavelength of 220 nm or less. In addition, a production yield of a protonic acid (H+xe2x80x94Yxe2x88x92) generated during the exposure is maintained to be high. The reaction occurring in the chemically amplified photoresist material or the acid catalyzed reaction in the resist resin catalyzed by the protonic acid (H+xe2x80x94Yxe2x88x92) is unchanged. The excellent transparency of the sulfonium salt compound of the present invention with respect to the ultraviolet ray having the wavelength of 220 nm or less allows the exposure light to uniformly penetrate deep in the resist film. Accordingly, the protonic acid is generated uniformly in a direction of depth of the film to provide a higher resolution during the transfer of the pattern.
In the sulfonium salt compound of the present invention, the substituted groups R1 and R2 in the sulfonium group may be independently a linear alkyl group such as methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group and heptyl group, a branched alkyl group such as isopropyl group, isobutyl group and tert-butyl group, a monocyclic cycloalkyl group such as cyclopentyl group, cyclohexyl group, cycloheptyl group and cyclooctyl group, and a bridged alkyl group such as norbornyl group, isobornyl group, adamantyl group, tricyclodecyl group and tetracyclododecyl group. In addition, R1 and R2 may bind to each other to form a ring or a bivalent group xe2x80x9cxe2x80x94R1xe2x80x94R2xe2x80x94xe2x80x9d containing the above carbon skeletons. An example of the bivalent group includes an alkylene group such as tetramethylene group and pentamethylene group and an oxoalkylene group such as 2-oxotetramethylene group and 3-oxopentamethylene group prepared by oxo-substitution of the alkylene group.
The ring formed by the bivalent group xe2x80x9cxe2x80x94R1xe2x80x94R2xe2x80x94xe2x80x9d with the sulfur xe2x80x9cSxe2x80x9d atom may be 4 to 8-membered ring, more preferably 5 or 6-membered ring. A preferred group is not restricted to those mentioned above.
An example of R3 to R6 in the cyclic group of the general formula (I) or the 1-oxoindan-2-yl group, the 1-tetralone-2-yl group or the 4-chromanone-2-yl group includes a hydrogen atom, a halogen atom, an alkyl group having 1 to 4 carbon atoms, and an alkoxy group having 1 to 4 carbon atoms. The halogen atom includes a fluorine atom, a chlorine atom, a bromine atom and an iodine atom. The alkyl group includes methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group and tert-butyl group. The alkoxy group includes methoxy group, ethoxy group and butoxy group. The preferable group for the R3 to R6 is not restricted thereto.
An example of the counter ion xe2x80x9cYxe2x88x92xe2x80x9d in the sulfonium salt compound of the general formula (I) is converted into the protonic acid (H+xe2x80x94Yxe2x88x92) during the exposure. Actual catalysis is determined according to the resist resin employed. Accordingly, the anionic component xe2x80x9cYxe2x88x92xe2x80x9d conventionally used in this kind of photo-acid generator can be selected in accordance with the resist resin. More concretely, a suitable example thereof includes perfluoroalkylsulfonate ion designated by a general formula (II) (wherein xe2x80x9cmxe2x80x9d is a positive integer from 1 to 9)
CmF2m+1SO3xe2x88x92xe2x80x83xe2x80x83(II)
such as CF3SO3xe2x88x92 (trifluoromethanesulfonate ion), C4F9SO3xe2x88x92 (nonafluorobutanesulfonate ion) and C8F17SO3xe2x88x92 (heptadecafluorooctanesulfonate ion). The preferable perfluoroalkylsulfonate ion is not restricted thereto. A suitable example of the anionic component xe2x80x9cYxe2x88x92xe2x80x9d further includes alkanesulfonate ion designated by a general formula (III) (wherein xe2x80x9ckxe2x80x9d is a positive integer from 1 to 9)
CkH2k+1SO3xe2x88x92xe2x80x83xe2x80x83(III)
such as CH3SO3xe2x88x92 (methanesulfonate ion), C2H4SO3xe2x88x92 (ethanesulfonate ion), C8H17SO3xe2x88x92 (1-octanesulfonate ion) and C9H19SO3xe2x88x92 (1-nonanesulfonate ion). The preferable alkanesulfonate ion is not restricted thereto.
A suitable example of the anionic component xe2x80x9cYxe2x88x92xe2x80x9d further includes benzenesulfonate ion and alkylbenzenesulfonate ion which includes p-toluenesulfonate ion and xylenesulfonate ion. The preferable alkylbenzenesulfonate ion is not restricted thereto.
A suitable example of the anionic component xe2x80x9cYxe2x88x92xe2x80x9d further includes fluorinated benzenesulfonate ion such as 4-fluorobenzenesulfonate ion and pentafluorobenzenesulfonate ion. The preferable fluorinated benzenesulfonate ion is not restricted thereto. A suitable example of the anionic component xe2x80x9cYxe2x88x92xe2x80x9d further includes fluorinated alkylbenzenesulfonate ion such as 4-trifluoromethylbenzenesulfonate ion and 3,5-bis(trifluoromethyl)benzenesulfonate ion. The preferable fluorinated alkylbenzenesulfonate ion is not restricted thereto.
A suitable example of the anionic component xe2x80x9cYxe2x88x92xe2x80x9d, further includes a fluorinated ion such as BF4xe2x88x92 (tetrafluoroborate ion), AsF6xe2x88x92 (hexafluoroarsenate ion) SbF6xe2x88x92 (hexafluoroantimonate ion) and PF6xe2x88x92 (hexafluorophosphate ion), and a halogenated ion such as Brxe2x88x92 (bromine ion) and Ixe2x88x92 (iodine ion). The preferable inorganic anion is not restricted thereto.
The counter ion represented by the xe2x80x9cYxe2x88x92xe2x80x9d in the sulfonium salt compound is, as described above, converted into the protonic acid (H+xe2x80x94Yxe2x88x92) during the exposure. The catalysis by the protonic acid must be maintained, and the counter ion is preferably selected such that the protonic acid is not vaporized nor scattered during the baking after the exposure.
The photoresist composition of the present invention may be positive or negative. The composition is the chemically amplified resist, contains, as the main components, the sulfonium salt compound as the photo-acid generator, the resin used as the resist and a solvent for dissolving these components. In the negative photoresist, a crosslinking agent for promoting the insolubilization of the resin at the exposed portion may be added similar to the conventional negative photoresist.
In the photoresist composition of the present invention, the sulfonium salt compound represented by the general formula (I) is used as the photo-acid generator wherein a single compound or a plurality of mixed compounds may be used. In the chemically amplified resist, the photo-acid generator is added and mixed at a specified ratio with respect to the resin, and the solvent has a roll of uniformly dissolving the resin, the photo-acid generator and the other additives. The solvent is suitably selected for adjusting the viscosity of the photoresist composition for the purpose of making the applicability in a specified range. Ordinarily, 0.2 to 30 weight parts, preferably 1 to 15 weight parts of the sulfonium salt compound represented by the general formula (I) with respect to 100 weight parts of the whole photoresist composition excluding the solvent is appropriate. The sufficient sensitivity is obtained at 0.2 weight part or more, and the pattern formation can be easily conducted. The uniform applied film can be formed and the scum is hardly generated after the development at 30 weight parts or less. The weight parts of the sulfonium salt compound may be selected depending on the kind of the resist resin employed and the acid catalyst reactivity of the protonic acid formed from the sulfonium salt compound.
In the positive photoresist composition, the resin is suitably used which is highly transparent to the ray having the wavelength of the exposing ray in the range from the far ultraviolet ray to the vacuum ultraviolet ray having a wavelength between 130 nm and 220 nm and may be solubilized in an alkaline developing solution by the function of the acid. Ordinarily, 60 to 99.8 weight parts, preferably 75 to 99 weight parts of the resin with respect to 100 weight parts of the whole photoresist composition excluding the solvent is appropriate.
The resin preferably used in the positive photoresist composition of the present invention includes resins represented by the following general formulae (IV), (V), (VI) and (VII).
The resin having the general formula (IV) is described in JP-A-2000-26446, wherein R7, R8, R9 and R11 are hydrogen atom or methyl group, R10 is a group decomposable by an acid, or a bridged cyclic hydrocarbon group having 7 to 13 carbon atoms and a group decomposable by an acid, R12 is a hydrogen atom, a hydrocarbon group having 1 to 12 carbon atoms or a bridged cyclic hydrocarbon group having 7 to 13 carbon atoms and a carboxyl group, x, y and z are any numbers satisfying the relation of x+y+z=1, 0 less than x less than 1, 0 less than y less than 1 and 0 less than z less than 1, and the weight average molecular weight of the polymer is 2000 to 200000. 
The resin having the general formula (V) is described in Japanese Patent No.2856116, wherein R13, R14 and R16 are hydrogen atom or methyl group, M is a group having a bridged cyclic hydrocarbon group having 7 to 13 carbon atoms, R15 is a group decomposable by an acid, R17 is a hydrogen atom or a hydrocarbon group having 1 to 12 carbon atoms, k, m and n are any numbers satisfying the relation of k+m+n=1, 0 less than k less than 1, 0 less than m less than 1 and 0xe2x89xa6n less than 1, and the weight average molecular weight of the polymer is 2000 to 200000. 
The resin having the general formula (VI) is described in Journal of Photopolymer Science and Technology, vol.10, no.4, p.545 to 550 (1997), wherein R18 is a methyl group or an ethyl group, R18 is a group having a lactone structure, a and b are any numbers satisfying the relation of a+b=1, 0 less than a less than 1 and 0 less than b less than 1, and the weight average molecular weight of the polymer is 2000 to 200000. 
The resin having the general formula (VII) is described in Journal of Photopolymer Science and Technology, vol.10, no.3, p.511 to 520 (1997), wherein c, d and e are any numbers satisfying the relation of c+d+e=1, 0 less than c less than 1, 0 less than d less than 1 and 0 less than e less than 1, and the weight average molecular weight of the polymer is 2000 to 200000. The resins other than the positive resins described herein may be used so long as they have similar high transparency and reactivity. 
In the negative photoresist composition, the resin is suitably used which is highly transparent to the ray having the wavelength of the exposing ray in the range from the far ultraviolet ray to the vacuum ultraviolet ray having a wavelength between 130 nm and 220 nm and may be insolubilized in an alkaline developing solution by the function of the acid. Ordinarily, 60 to 99.8 weight parts, preferably 70 to 99 weight parts of the resin with respect to 100 weight parts of the whole photoresist composition excluding the solvent is appropriate.
The resin preferably used in the negative photoresist composition of the present invention includes resins represented by the following general formulae (VIII) and (IX).
The resin having the general formula (VIII) is described in Journal of Photopolymer Science and it Technology, vol.12, no.3, p.487 to 492 (1999), wherein f, g and h are any numbers satisfying the relation of f+g+h=1, 0 less than f less than 1, 0 less than g less than 1 and 0 less than h less than 1, and the weight average molecular weight of the polymer is 2000 to 200000. 
The resin has the general formula (IX) wherein q, r and s are any numbers satisfying the relation of q+r+s=1, 0 less than q less than 1, 0 less than r less than 1 and 0 less than s less than 1, and the weight average molecular weight of the polymer is 2000 to 200000. The resins other than the negative resist resins described herein may be used so long as they have similar high transparency and reactivity. 
A crosslinking agent for promoting an insolubilization reaction of the resin at the exposed portion may be added. An example of the preferable crosslinking agent includes a urea-melamine-based crosslinking agent such as hexamethoxymethyl-melamine, 1,3,4,6-tetrakis (methoxymethyl)glycoluril, 1,3-bis(methoxymethyl)-4,5-bis(methoxymethyl)-ethyleneurea and 1,3-bus(methoxymethyl)urea, and a polyvalent alcohol such as 2,3-dihydroxy-5-hydroxymethylnorborane, 1,4-cyclohexandimethanol and 3,4,8(9)-trihydroxytricyclodecane. The preferable crosslinking agent is not restricted thereto. A single crosslinking agent or a plurality of mixed crosslinking agents may be used.
The photoresist composition of the present invention contains a proper amount of the solvent in addition to the resin and the sulfonium salt compound. The solvent may be any organic solvent provided that it uniformly dissolves the components of the resin and the sulfonium salt compound and can form a uniform applied film by using the photoresist composition by means of a spincoat method. A single solvent or a plurality of mixed solvents may be used. A concrete example thereof includes an alcohol such as n-propyl alcohol, isoproryl alcohol, n-butyl alcohol and tert-butyl alcohol, an ester such as methylcellosolve acetate, ethylcellosolve acetate, proryleneglycol monoethylether acetate, methyl lactate, ethyl lactate, 2-methoxybutyl butyrate, 2-ethoxyethyl butyrate, methyl pyruvate, ethyl pyruvate, methyl 3-methoxy propionate and ethyl 3-methoxy propionate and, a cyclic ketone or alcohol such as N-methyl pyrrolidinone, cyclohexanone, cyclopentanone and cyclohexanol, and a keone such as methyl ethyl ketone and a glycol ether such as 1,4-dioxane, ethyleneglycol monomethyl ether, ethyleneglycol monomethyl ether acetate, ethyleneglycol monoethyl ether, ethyleneglycol monoisopropyl ether, diethyleneglycol monomethyl ether and diethyleneglycol dimethyl ether. The preferable solvent is not restricted thereto.
The fundamental components of the positive and the negative photoresist compositions of the present invention are the sulfonium salt compound having the general formula (I), the resin and the solvent. However, a dissolving inhibitor, a crosslinking agent, a basic compound, a surface-active agent, a pigment, a stabilizer, an application modifier and a dye may be added thereto depending on necessity.
A method for patterning of the present invention is to transfer a mask pattern on a photoresist applied film utilizing the positive or the negative photoresist composition and the exposing ray selected from 130 to 220 nm. In the method, the steps of applying the photoresist, and of baking the composition before and after the exposure are essentially the same as those of the patterning using the conventional chemically amplified photoresist. The acid catalyzed reaction by the protonic acid produced by the exposure is substantially the same as that employing a triphenylsulfonium salt compound as a photo-acid generator (sensitized agent).